Definitely looks like a fungus ( P.M.) to me. I have seen worse. I had this same problem with my zucchini last season. I will tell you this, I had very good luck with baking soda! Mine still produced some zucchini's but not what it should have. Like others mentioned, make sure you get rid of old leaves. When its time to dig up the crop I would remove the area soil and replace it with new stuff to keep the contaminated soil to a minimum,. [links removed by admin]
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